1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of selectively directing a mobile station to retry system access in a radio telecommunication system.
2. Description of Related Art
Existing cellular radio telecommunication systems perform a function known as directed retry. If a particular cell is congested (i.e., all of the cell's traffic channels are occupied) when a mobile station (MS) attempts to access the system, the serving mobile switching center (MSC) may direct the MS to retry the access in a neighboring cell. When a directed retry is performed, there can be an adverse impact on the level of co-channel interference when the MS begins operating in a different cell than the cell with the best signal strength. This, in turn, may cause a decrease in the general voice quality achieved in the system.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 5,509,051 to Barnett et al. (Barnett); U.S. Pat. No. 5,287,545 to Kallin (Kallin); and U.S. Pat. No. 5,497,504 to Acampora et al. (Acampora); and UK Patent Application GB 2,287,614A to Ueno et al. (Ueno) discuss subject matter that bears some relation to matters discussed herein.
Barnett discloses a method of prioritizing neighboring cells for handoff in a cellular telecommunication system. In FIG. 3, the method is shown to involve comparing the signal strength in the serving cell to the signal strength in each neighboring cell, and establishing a graph with a handoff region. Neighboring cells are then prioritized by signal strength, with cells falling to the right side of the graphed handoff region having higher priority for handoff. Barnett, however, does not teach or suggest a method within a mobile switching center (MSC) which collects signal strength measurements (of the serving cell and of neighboring cells) both from MSs which are involved in calls and from MSs which are currently camped on the Digital Control Channel (DCCH) waiting for system access. Likewise, Barnett does not teach or suggest a method which utilizes this measurement information to either handoff MSs currently involved in calls or redirect the access of camped MSs to target cells in such a way as to minimize co-channel interference in the cellular system.
Kailin discloses a method and apparatus for advanced directed retry in which a directed retry message is sent to a mobile station which attempts to access a cellular system in a first cell which is congested. The mobile station then attempts to access the system in a second cell, but if a traffic channel becomes available in the first cell, the call is established in the first cell, thereby reducing interference in the system. However, Kallin does not teach or suggest a method which collects signal strength measurements (of the serving cell and of neighboring cells) both from MSs which are involved in calls and from MSs which are currently camped on the DCCH waiting for system access. Additionally, Kallin does not teach or suggest a method which utilizes this measurement information to calculate whether to hand off a MS currently involved in a call or redirect an accessing MS to a target neighbor cell in such a way as to minimize co-channel interference in the cellular system.
Acampora discloses a system and method for controlling admission of new calls to a cellular telecommunication system. New calls are admitted or rejected on the basis of a number of factors such as classes of calls, number of calls in each class in each cell-cluster, traffic characteristics, quality-of-service requirements for each class, and scheduling policies at each base station. However, Acampora does not teach or suggest a method which collects signal strength measurements both from MSs which are involved in calls and from MSs which are currently camped on the DCCH waiting for system access. Likewise, Acampora does not teach or suggest a method which then calculates whether to hand off a MS currently involved in a call or to redirect an accessing MS to a target neighbor cell in such a way as to minimize co-channel interference in the cellular system.
Ueno discloses a method which enables a mobile station user to determine whether a handoff is to be performed in a cellular telecommunications network. A signal transmitted from the mobile station to the network causes the network to switch or hold the voice channel accordingly. However, Ueno does not teach or suggest a method which collects signal strength measurements both from MSs which are involved in calls and from MSs which are currently camped on the DCCH waiting for system access. In addition, Ueno does not teach or suggest a method which then calculates whether to hand off a MS currently involved in a call or to redirect an accessing MS to a target neighbor cell in such a way as to minimize co-channel interference in the cellular system.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of collecting signal strength measurements from MSs which are involved in calls and from MSs which are currently camped on the DCCH waiting for system access. In addition, the method would then calculate whether to hand off a MS currently involved in a call or to redirect an accessing MS to a target neighbor cell in such a way as to minimize co-channel interference in the cellular system. The present invention provides such a method.